1. Field of the Invention
The invention relates generally to aircraft. More specifically, the invention relates to ice protection systems for aircraft, including ice protection systems that utilize piccolo tubes to heat, among other potential elements, the leading edge of slats, wing and horizontal stabilizer structures with hot gases.
2. Description of the Related Art
Ice protection systems that utilize hot gases to heat the leading edge of slats and wing structures have been described for use in aircraft. The ice protection systems often use a tube, commonly known as piccolo tube because of numerous spray holes in the tube, to direct hot gas, often from engine bleed air, to the leading edge of the structure to be heated. The hot gas is then channeled to the appropriate area of the surface through the holes in the piccolo tube.
The piccolo tubes are often mounted on the internal structures of the leading edge of the structure to be heated, and the tubes and the spray holes in the tubes are separated by a distance from the surface to be heated. The hot gas delivered by the piccolo tube must be channeled to the appropriate surface of the leading edge. In the past this has occasionally been accomplished by using structures built into the interior or the surface of the leading edge or the piccolo tube itself to maintain the distance from the leading edge surface to the tube and to direct the flow of hot gas.
Composite materials are commonly used to form the piccolo tube in the slat, with structures built into the surface of the tube for the purpose of directing the hot gas across the slat surface and for maintaining the fixed separation between the piccolo tube and the slat. Piccolo tubes formed from composite materials may degrade after continued exposure to the pressure, elevated temperatures and moisture associated with the operation of the piccolo tube. The delaminated tube and resulting debris may not allow sufficient flow downstream to provide the desired ice protection. Such failures often occur in the higher pressure and temperature sections of the piccolo tube, such as near the hot gas inlet.
Piccolo tubes formed from metal better resist the harsh conditions, but have high rates of heat transfer at the locations of contact with the slat, leading to localized heating at the point of contact, and relatively less heating across the other surface area of the slat.
The anti-ice piccolo tube standoff described herein allows for the use of a metal piccolo tube without the excessive heat transfer or other problems related to the use of metal piccolo tubes in other designs.